Drawing instruments for drawing ellipses



Nov. 7, 1961 P. F. BOEHM DRAWING INSTRUMENTS FOR DRAWING ELLIPSES 2 Sheets-Sheet 1 Filed Sept. 23, 1959 United States Patent 3,007,247 DRAWING INSTRUMENTS FOR DRAWING ELLIPSES Paul F. Boehm, 47-49 194th St., Flushing 58, N.Y. Filed Sept. 23, 1959, Ser. No. 841,872 7 Claims. (Cl. 33-1) The present invention concerns drawing instruments, and more particularly instruments of the template or stencil type which are used for tracing typical curves from a correspondingly shaped edge of the stencil or template by guiding a line producing implement along such edge.

The instrument according to the invention is specifically designed for drawing ellipses which are frequently needed in the production of three-dimensional illustrations as in perspective or raxonometric drawings.

Ordinary ellipse templates or stencils are provided with one or more cutouts of elliptic shape related to desired projection angles which determine the particular shape of the ellipses, and for obvious reasons. each template contains a selection of different sizes of ellipses, differing by arbitrary increments. Frequently the particular selection of sizes entails difficulties for the user of the template since often ellipse sizes are needed in his work which are not contained in the particular selection embodied in the template.

It is therefore a main object of this invention to provide a drawing instrument for drawing ellipses which is steplessly adjustable for any size of ellipses of a particular projection, between a minimum and a maximum size.

It is a further object of the invention to provide an instrument of the type set forth which is compact and simple in construction and operation.

It is a further object of the invention to provide an instrument of this type which is particularly suited for use in connection with axonometric drawing.

With above objects in view a drawing instrument having at least one template member for drawing ellipses according to the invention comprises, in combination, a frame having \a first axis and a second axis perpendicular thereto in one common plane and adapted to be placed on a drawing surface parallel with said plane to be supported thereby in a position in which said axes are in alignment, respectively, with the major and minor axes of the ellipse to be drawn, control means mounted on said frame for adjusting a template member of the instrument to desired ellipse sizes, and at least one segmental rigid template member shiftably and turnably mounted on said frame and having one of its edges formed as at least one quarter of the contour, between its intersection points with its major and minor axes, respectively, of the the largest ellipse to be drawn by tracing said edge, and operatively connected with said control means for being moved by operation of said control means between a plurality of selectable positions in which that point of said edge which is to correspond to the point of maximum radius of curvature of a selected ellipse to be drawn is located on said second axis of said frame with said radius in alignment therewith, and at a distance from the intersection of said axes equal to one-half of the minor axis of the particular ellipse to be drawn.

Additional objects and advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of preferred embodiments thereof in connection with the accompanying drawings in which:

FIG. 1 is a plan view of an instrument with the cover removed to show other details, the upper half being substantially omitted as it is identical with the lower half illustrated;

FIG. 1a is similar, but shows a different adjustment of the instrument;

FIG. 2 is an elevation of the instrument of FIG. 1 including the cover;

FIG. 3 is a. sectional elevation of the same instrument, the section being taken along line ABC of FIG. 1;

FIG. 4 is a sectional end view, the section being taken along line FBEGD of FIG. 1;

FIG. 5 is a partial sectional end View, the section being taken along line MM of FIG. 1;

FIG. 6 is a partial sectional view taken along line LL of FIG. 1;

FIG. 7 is another partial sectional view taken along line HIIK of FIG. 1; and

FIG. 8 is a plan view of a modification of the instrument of FIG. 1.

Referring now to FIGS. 1-7, the instrument comprises a frame 1 which in this example'is a circular disc of sheet material having the center B in which a first axis C and a second taxis B intersect each other at 90 and has a central, preferably elliptical opening indicated at 1' in full and partly in dotted lines in FIG. 1 and recognizable in the sectional views FIGS. 3 and 4. Along the rim of the frame 1 threaded holes, e.g. by means of flat nuts 7 attached to the rim, are provided for enabling the cover 2 to be attached to the frame 1 by screws 7.

Two control rings 3 and 3' are mounted for rotation about the center point B, the lower ring 3' being supported slidingly on the upper surface of the frame disc 1, the upper ring 3 being slidingly supported on top of ring 3 with the interposition of members 14, 14, described below, which act as spacers as can be seen clearly in FIGS. 3 and 4. The rings 3 and 3 may be held in concentric position With respect to center B by any suitable means. As an example, FIGS. 1 and 7 show a block 17 attached to the frame disc 1 and a leaf spring 18 attached to the block 17 and pressing in radial direction against the inner edges of both rings 3 and 3', hereby urging them against abutment pins or studs 8 attached to the frame disc 1 in suitable positions for guiding the outer circular edges of rings 3 and 3. In order to maintain the rings 3 and 3 in proper superposed position on the frame disc 1, three blocks 15 (only two being shown in FIG. 1) are mounted on the frame disc 1 for holding each a leaf spring 16 which bears on the top surface of the upper ring 3 as shown in FIG. 6 in greater detail.

Each of the control rings 3 and 3 is provided along a portion of its outer edge as seen at the right hand of FIG. 1 with a series of gear teeth 3a and 3a (see FIG. 3) which are permanently in mesh with drive gears 6 and 6', respectively, for being rotated in opposite directions whenever the gear 6 is turned by means of the control 'knob 5 mounted on the shaft or rather axle pin 4 which is, in turn, attached to the base frame plate 1. The second gear 6' is independently mounted for rotation about a second pin 4' likewise attached to base 1. As can be seen from 'FIGS. 3 and 5, the respective axial lengths ofthe gears 6 and 6' and their relative positions with respect to the control rings 3 and 3', respectively, are such that the upper half of gear 6 meshes with the gear segment 3a of ring 3 and with the upper half of gear 6', while the latter meshes with its lower half with the gear segment 3a of ring 3'. Consequently, when gear 6 is turned in one direction it will drive the ring 3 in one direction and at the same time drive the gear 6 in a direction oppositeto its own direction of turn, so that the second ring 3 is turned by the gear 6' in a direction opposite to said one direction of turn of ring 3. The

" angular displacements of the control rings 3 and 3 are always equal and opposite to each other.

, brackets 14' are attached to the upper face of the lower control ring 3' (only one of these brackets being visible in FIG. 1). The brackets 14 and 14' are angularly spaced from each other and of even thickness so that they act as spacers between the rings 3 and 3. As will be explained later, each ring 3, 3' has a maximum position and a minimum position which refers to the size of ellipses that can be drawn in either position. Accordingly, the brackets 14, 14 have a maximum position and a minimum position determined by the amount of turn of the rings from one of said positions toward the other. It should be understood that for the purpose of explanation and of showing certain details, in FIG. 1 the brackets 14 and 14' are shown in their maximum position, while in FIG. la the brackets 14, 14' are shown in their minimum position, the maximum position being indicated in FIG. 1 by the line AB, but for reasons stated above, the rings and brackets will always be in relatively equal positions of symmetry with respect to the center axis C.

Each of the brackets 14, 14' carries at its radially inward projecting end a control pin projecting downward as shown in FIG. 3 which engages a cooperating guide slot 12 of the associated segmental template member 9, 9, 9a, 9a, respectively, described below. Through this engagement the turning movement of the control rings 3, 3 is transmitted to the template members just mentioned so as to cause the latter to follow rotarily the movement of the associated control ring and bracket.

Each of the segmental template members 9 and 9a forms a pair with the other and is substantially identical with the other, and the same is true for the other pair 9' and 9a. However, the template members of one pair are oppositely symmetrical with those of the other pair, as can be gathered from FIG. 1. Each template member has an inner tracing edge d which is formed as onequarter of the largest ellipse to be drawn with the instrument, the quarter being limited by the corresponding major and minor axes. Whenever all four members 9, 9', 9a, 9a are in their maximum position, the four edges d together constitute the shape of the entire maximum ellipse, as can be seen from FIG. 1. In this position a second edge 10 of each member abuts against the respective edge 10 of the adjacent member, i.e. member 9 against member 9, and member 9a against member 9a, the abutting line coinciding in this position with the major axis of the ellipse and with the center axis B. The other ends of the edges d extend tangentially beyond the point of intersection of edge d with the minor axis or central axis C because the template members are provided with an extension portion 10', those of adjacent members overlapping each other as shown. Since the template members are preferably made of very thin sheet metal stock, about .005 thick, the overlapping does not interfere with the operation of the tracing scriber.

The outer or rear edges of the template members 9, 9', 9a, 9a are formed as curved cam contours e and f which abut for the purpose of guidance against fixed guide pins a and b as shown particularly in FIG. 1. Only one pin a and two pins b are visible in FIG. 1, but there is another pin a and two more pins b in the upper portion of the instrument, symmetrically therewith relative to the central axis B. Springs 13 are connected between the pertaining control ring 3, 3 and a suitable point of the respective template member for urging the latter in outward direction against the guide pins a and b. The curvature and location of the cam edges e and f, in relation to the inner edge d, the position of the pins a and b with respect to the main axes B and C, are so chosen that when the control rings 3, 3 are rotated and the template members are simultaneously moved angularly about varying centers of rotation while sliding along the fixed pins a and b with their cam edges e and say between the maximum position and the minimum position, then the ellipse contour edge d will, for all four template members, consecutively assume positions in which portions thereof constitute the ellipse contour of any size smaller ellipses starting from the intersection point thereof with its minor axis, this particular point falling on the central axis C and being the point where the radius of curvature of the particular ellipse is at a minimum so that the radius of this minimum curvature coincides with axis C and the respective distance of that point is equal to the respective minor axis measured from the center point B.

FIG. 1 shows for the template members 9, 9', 9a, 9a their maximum position and FIG. la shows their minimum position. In any intermediate position said edge portions of d constitute portions of the contour of the desired ellipse, considering the four template members as acting together. It can be seen that the template members overlap to an increasing degree as they move toward the minimum position but without interfering with the accessibility of the contour portions d.

The form of the cam edges e and f and the corresponding positions of the guide pins a and b can be calculated although the calculation is extremely involved. A more practical way is the following. A plurality of ellipses of a chosen projection and of various sizes varying between a selected maximum and a selected minimum are drawn with conventional means, concentrically in relation to perpendicular axes B and C representing the direction of the major and minor axes thereof, respectively. A piece of flat material, e.g. tracing paper is cut so as to obtain an edge equal to the quarter contour of the maximum ellipse between major and minor axes. On the surface on which the plurality of ellipses have been drawn a point a is marked on the axis line C. Tentatively, a point b is marked on the same surface. Now the cut out tracing paper is placed consecutively in positions in which its elliptic edge registers with corresponding portions of the various drawn ellipses, in positions meeting the above conditions, and in every position of the tracing paper pattern the location of the points a and b appearing through the paper are marked thereon. Connecting these marked points furnishes the shape of the cam edges e and f.

It can be seen that, as FIG. la shows, the originally abutting edges 10 of adjacent template members 9, 9 or 9a, 9a move angularly apart toward a position marked (10) as the template members move from maximum position to minimum position. This means that both sides of the major axis or center line B a small gap develops between the corners where the respective edges d and 10 meet. This could be avoided if the edge d were continued with decreasing radius of curvature beyond said points so that these portions of adjacent template members also overlap. However, such extensions would interfere with tracing a continuous ellipse of the maximum size past the point of minimum curvature. This would not render the instrument useless because in the small area of interference the tracing could be stopped, and the gap filled in later by a small circular arc of suitable radius. This is being done with many types of ellipse templates.

However, according tothe invention means are provided to overcome this difficulty. A thin resilient wire 19 is attached to two of the template members, e.g. 9' and 9a so that they extend tangentially to the point of smallest curvature of the edge d in direction toward the adjacent template member 9 and 9a, respectively, overlapping the latter. Next to the above mentioned corner an abutment or guide member 20 is attached to the members 9 and 9a, respectively. This may be a small pin or just a bent-up portion of the material of these members. Its position is so that the respective wire 19 being originally in tangential position by leaning against that particular pin 20 is positioned so as not to interfere with tracing the maximum ellipse. As the template members 9, 9', 9a, 9a are moved into other positions toward the minimum position, the members move spacing the edges 10 from each other, but the wire 19 remaining tangential to member 9' and 9a, respectively, is forced by the opposite pin 20 to bend, as shown in FIG. In, so that its free end extends tangentially to the point of minimum curvature of the contours d of the members 9 and 9a, respectively. The curvature of the wire is satisfactorily close to the elliptic curvature in the particular small portion of the total ellipse.

In practice, a draftsman desiring to draw an ellipse of a particular size with the instrument according to the invention will first draw the major and minor axes of that ellipse, then locate the whole instrument on the drawing board so that the instrument axes B and C register with the drawn major and minor axes, respectively. Then he has to mark on the drawing paper only two contour points of the desired ellipse, which points may be, but do not have to, located on the major and minor axes. Actually even one such point would be sufficient.

By turning the control knob in one or the other direction the template members 9, 9, 9a, 9a will be moved from whatever position thereof into one in which their inner contour edges d, or at least one of them register with the premarked contour point of the desired ellipse. Now the whole ellipse can be traced in one swing along the combined edge portions d including the wire bridges 19.

It is advisable to provide the instrument with a cover 2 as shown and having an inner elliptic opening with turned down rim 2a the contour whereof is of course an ellipse larger than the maximum ellipse to be drawn with the instrument. Advantageously the rim 2a is lined inside with a strip 2b of elastic material as for instance trifluoroethylene which is not hygroscopic and has a very low friction coefficient, so that it can be caused to bear with slight pressure down on the upper surfaces of the template members 9, 9, 9a, 9a so as to hold them down on the supporting top surface of the frame base plate 1.

Referring now to FIG. 8, a modified embodiment of the invention is shown in which the entire assembly as illustrated by FIGS. l7 is mounted on an outer frame preferably of transparent material, marked 21. This outer frame 21 serves to correctly orient the frame 1, i.e. the whole instrument on a drawing surface particularly if the instrument is to be used in connection witih axonometric drawing. In this type of three-dimensional or pictorial illustration the necessary ellipses have to be oriented in a predetermined manner with respect to the axes of the particular axonometric projection. Usually one axis is called the vertical axis and is perpendicular to a horizontal reference line on the drawing or drawing board. The other two axes are inclined against the horizontal to a degree characteristic of the chosen axonometric projection.

The embodiments illustrated in FIG. 1 and in FIG. 8 are suited for isometric drawing. Consequently, the outer frame 21 is shaped as a polygon having a base edge 22, a left 23 perpendicular to the edge 22, two upper slanting edges 24, 25 which are inclined 30 in opposite directions, respectively, against the base edge 22, and two auxiliary base edges 26 and 27 which include an angle of 60, in opposite directions, respectively, with the base edge 22. The instrument is mounted in the frame 21 in a position in which its main axis B, coordinated with the major axes of the ellipses to be drawn by means of the template members 9-9a', is oriented parallel with the edge 27, i.e. 60 against 22, and the second main axis C is parallel with the edge 25 i.e. 30 against 22. Of course the axis lines B and C may be marked on the transparent frame 21 for registering with major and minor axes of ellipses as explained above. However, in axonometric drawing little attention is paid to the major and minor axes, instead reference is had to the axonometric axes of the respective ellipses. In the case of isometric drawing the axonometric axes extend at 30 to the major axis of the ellipses. Therefore, the frame 21 is marked with index lines A and A" which are oriented as the isometric axes of the ellipse opening in the center, namely parallel with the edges 23 and 24, respectively. Thus, if the axonometric, or in this case, isometric axes are drawn on the drawing surface, the instrument may be oriented and registered properly by lining up the axis markings A and A" with the respective center lines. However, it can be seen that the correct orientation is immediately achieved if the base edge 22 is placed against a horizontal T-square or straightedge.

Since the edges 23, 24, 25 extend, by definition, parallel with the axes of the isometric system, it is most convenient to provide these three edges with graduations, e.g. full scale inch graduations as shown so that the user of the instrument may use the three edges for drawing lines forming part of the isometric drawing, lay out dimensions or measure dimensions appearing in direction of the axes etc.

Since an isometric representation of a three-dimensional object contains configurations in three main planes, it must be expected that ellipses have to be produced in proper positions characteristic of the particular plane in which such an ellipse is situated. If the three main planes, referring to the faces of a cube as an example, are called the right-hand side, the left-hand side and the top, then the edge 22 would, if placed against the T-square or straightedge for horizontal orientation, orient the ellipse template assembly of the instrument in correct orientation for the right-hand side, but if the frame 21 is turned and placed with the edge 27 against the T-square then the ellipse assembly is oriented for the top, and finally, if the instrument is turned more and placed with the edge 26 against the T-square then the ellipse assembly is oriented for the left-hand side. In all these cases the axis lines through A and A" extend in the direction of the two main axes pertaining to the particular plane.

While I have described and shown preferred embodiments of my invention, I wish it to be understood that I wish not to be limited to any particulars or details of the described and shown construction as those skilled in the art may introduce variations and modifications without departing from the gist of my invention.

What I claim is:

l. A drawing instrument having at least one template member for drawing ellipses, comprising, in combination, frame means having a first axis and a second axis perpendicular thereto in one common plane and being adapted to be placed on a drawing surface parallel with said plane to be supported thereby in a position in which said axes are in alignment, respectively, with the major and minor axes of the ellipse to be drawn, control means mounted on said frame means for adjusting a template member of the instrument to desired ellipse sizes, and at least one rigid segmental template member shiftably and turnably mounted on said frame means and having one of its edges formed as at least one quarter of the contour between its intersection points with its major and minor axes, respectively, of the largest ellipse to be drawn by tracing said edge, and operatively connected with said control means for being moved by operation of said control means between a plurality of selectable positions in which that point of said edge which is to correspond to the point of maximum radius of curvature of a selected ellipse to be drawn is located on said second axis of said frame means with said radius in alignment therewith, and at a distance from the intersection of said axes equal to one-half of the minor axis of the particular ellipse to be drawn.

2. A drawing instrument having template members for drawing ellipses, comprising, in combination, frame means having a first axis and a second axis perpendicular thereto in one common plane and being adapted to be placed on a drawing surface parallel with said plane to be supported thereby in a position in which said axes are in alignment, respectively, with the major and minor axes of the ellipse to be drawn, control means mounted on said frame means for adjusting the template members of the instrument to desired ellipse sizes, and two pairs of substantially identical rigid segmental template members shiftably and turnably mounted on said frame means and each having one of its edges formed as at least one quarter of the contour between its intersection points with major and minor axes, respectively, of the largest ellipse to be drawn by tracing said edge, and operatively connected with said control means for being moved by operation of said control means between a plurality of selectable positions in which that point of said edge which is to correspond to the point of maximum radius of curvature of a selected ellipse to be drawn is located on said second axis of said frame means with said radius in alignment therewith, and at a distance from the intersection of said axes equal to one-half of the minor axis of the particular ellipse to be drawn, the template members of each pair being arranged relatively in symmetry with both said axes, the template members of one pair thereof being mirror-reversed duplicates of template members of the other pair, each of said template members having a first side edge portion extending from the point of minimum radius of curvature of said one edge substantially radially with respect to the center of said frame means, said first side edge portions of neighboring template members abutting each other when said template members are positioned for the largest ellipse to be drawn, and each of said template members having an extension portion with a second side edge portion extending from the point of maximum radius of curvature of said one edge thereof, said extension portions of neighboring template members overlapping each other.

3. A drawing instrument as claimed in claim 2, bridging edge members being attached to each template member of one pair thereof extending from said point of minimum radius of curvature tangentially to said curva' ture of minimum radius over the corresponding portion of the neighboring template member of the other pair thereof, abutting means being provided on said neighboring template member for forcing said bridging edge member to bend when said template members are moved from the position in which first side edge portions abut each other to other selectable positions and to continue bridging the contour of said one edge of one template member to the corresponding contour of said one edge of the neighboring template member.

4. A drawing instrument as claimed in claim 3, wherein said control means comprise two control ring means arranged for being rotatable about said intersection point of said axes of said frame means and supported by the latter, and operating means for causing rotation of said ring means in respectively opposite directions simultaneously through identical angular amounts, each of said template members having curved outer cam edge portions, and cam guiding means being mounted on said frame means for cooperating with said cam edge portions of said template members, respectively, during their movements, biasing means for holding said cam edge portions in contact with said cam guiding means, and cooperating means on said control ring means and said template members, respectively, for transmitting a turning movement of one of said control ring means to one pair of said template members and from the other one of said control ring means to the other pair of said template members whereby said template members are simultaneously moved between said selectable positions by operation of said control means.

5. A drawing instrument as claimed in claim 1, including an outer frame plate attached to said frame means and comprising a transparent portion surrounding said frame means, said transparent portion being formed with edges oriented with respect to said axes of said frame means so as to cause said last mentioned axes to be oriented correctly within an axonometric system corresponding to the shape of the ellipses determined by said contour of said one edge of said template members, when said edges of said transparent frame portion are placed, respectively, in alignment with the horizontal reference line of the drawing to which the ellipse to be drawn refers.

6. A drawing instrument as claimed in claim 5, wherein said transparent frame portion is provided with other outer edges oriented with reference to said edges of said frame portion so as to extend in the directions, respectively, of the axonometric axes of said axonometric system.

7. A drawing instrument as claimed in claim 6, where in said other outer edges are provided with graduations corresponding to the scales applying to said axes of said axonometric system.

References Cited in the file of this patent UNITED STATES PATENTS 950,285 Harper Feb. 22, 1910 

